The invention relates to the production of tert. butyl ethyl ether (TBEE).
It is known that tert. butyl ethyl ether, like tert. butyl methyl ether (TBME), can be used as a high octane rating additive for reduced lead or lead-free gasoline TBEE can be added to gasoline in concentrations ranging e.g. up to approximately 15% by volume.
One process for the production of TBME consists of carrying out a reaction of adding methanol to isobutylene, e.g. contained in a C.sub.4 fraction from a catalytic cracking or steam cracking stage. After reaction, the residual methanol is generally separated by azeotropic distillation with the C.sub.4 hydrocarbons, which makes it possible to obtain in a relatively easy manner the TBME with an appropriate level of purity for adding to gasoline.
The production of TBEE can be carried out by an identical process, where the methanol is replaced by ethanol. Such a process is e.g. described in "ETBE, un avenir pour l'ethanol" by A. Forestiere, B. Torck and G. Pluche, communication at the Conference on the Biomass for Energy and Industry, Lisbon, Oct. 9-13 1989 and "MTBE/ETBE, an Incentive Flexibility for Refiners" by A. Forestiere et al, communication at the Conference on Oxygenated Fuels in Europe, London May 22/23 1990.
However, in such a process and unlike in the case of TBME, after the elimination of the C.sub.4 hydrocarbons, almost all the residual ethanol is mixed with the TBEE produced. The existence of an ethanol-TBEE azeotrope with 21% by weight ethanol at atmospheric pressure and boiling at 66.6.degree. C. makes it difficult to separate the TBEE with a level of purity adequate for satisfying specifications regarding the ethanol content in gasoline. Thus, the ethanol content of TBEE must generally be between 0.5 and 10% by weight. Advantageously, the TBEE must be purified to less than 2% by weight ethanol in order to be transferred to the refinery.